part 2

2024/Cargo.lock

@@ -51,6 +51,12 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "autocfg"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ace50bade8e6234aa140d9a2f552bbee1db4d353f69b8217bc503490fc1a9f26"
+
 [[package]]
 name = "bitflags"
 version = "2.6.0"
@@ -186,6 +192,7 @@ dependencies = [
  "divan",
  "helper",
  "nom",
+ "num-integer",
  "smallvec",
 ]
 
@@ -273,6 +280,24 @@ dependencies = [
  "minimal-lexical",
 ]
 
+[[package]]
+name = "num-integer"
+version = "0.1.46"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7969661fd2958a5cb096e56c8e1ad0444ac2bbcd0061bd28660485a44879858f"
+dependencies = [
+ "num-traits",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.2.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "071dfc062690e90b734c0b2273ce72ad0ffa95f0c74596bc250dcfd960262841"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.92"

2024/day08/Cargo.toml

@@ -10,6 +10,7 @@ nom.workspace = true
 helper.workspace = true
 divan.workspace = true
 smallvec = "1.13.2"
+num-integer = "0.1.46"
 
 [[bench]]
 name = "benches"

2024/day08/src/lib.rs

@@ -244,7 +244,7 @@ fn part1_arrayvec(input: &str) -> u64 {
         }
     }
     impl<'a> IntoIterator for &'a Arrayvec {
-        type IntoIter = std::slice::Iter<'a,Coods>;
+        type IntoIter = std::slice::Iter<'a, Coods>;
         type Item = &'a Coods;
         fn into_iter(self) -> Self::IntoIter {
             unsafe { self.elems.get_unchecked(0..self.len).iter() }
@@ -312,8 +312,79 @@ fn part1_arrayvec(input: &str) -> u64 {
         .count() as u64
 }
 
-fn part2(_input: &str) -> u64 {
-    0
+fn part2(input: &str) -> u64 {
+    let mut all_antennas = [const { vec![] }; 256];
+
+    let mut width = 0;
+
+    let mut row = 0;
+    let mut col = 0;
+    for cell in input.bytes() {
+        if cell == b'\n' {
+            row += 1;
+            width = col;
+            col = 0;
+        } else if cell != b'.' {
+            all_antennas[cell as usize].push((col as i64, row as i64));
+            col += 1;
+        } else {
+            col += 1;
+        }
+    }
+
+    let height = row;
+
+    let mut is_antinode = vec![false; width * height];
+    let all_antennas = &all_antennas[b'0' as usize..b'z' as usize];
+
+    for antennas in all_antennas {
+        for (i, &a) in antennas.iter().enumerate() {
+            for (j, &b) in antennas.iter().enumerate() {
+                if i >= j {
+                    continue;
+                }
+
+                let mut diff = (a.0 - b.0, a.1 - b.1);
+
+                loop {
+                    let gcd = num_integer::gcd(diff.0, diff.1);
+                    if gcd == 1 {
+                        break;
+                    }
+                    diff = (diff.0 / gcd, diff.1 / gcd);
+                }
+
+                let mut antinode = a;
+                while (0..(width as i64)).contains(&antinode.0)
+                    && (0..(height as i64)).contains(&antinode.1)
+                {
+                    unsafe {
+                        *is_antinode.get_unchecked_mut(
+                            (antinode.0 as usize * width) + antinode.1 as usize,
+                        ) = true;
+                    }
+                    antinode = (antinode.0 + diff.0, antinode.1 + diff.1);
+                }
+
+                let mut antinode = a;
+                while (0..(width as i64)).contains(&antinode.0)
+                    && (0..(height as i64)).contains(&antinode.1)
+                {
+                    unsafe {
+                        *is_antinode.get_unchecked_mut(
+                            (antinode.0 as usize * width) + antinode.1 as usize,
+                        ) = true;
+                    }
+                    antinode = (antinode.0 - diff.0, antinode.1 - diff.1);
+                }
+            }
+        }
+    }
+
+    is_antinode
+        .iter()
+        .filter(|is_antinode| **is_antinode)
+        .count() as u64
 }
 
 helper::tests! {
@@ -324,7 +395,7 @@ helper::tests! {
     }
     part2 {
         small => 34;
-        default => 0;
+        default => 949;
     }
 }
 helper::benchmarks! {}